The present invention relates to the field of power systems. In particular, the present invention relates to a device for managing variations in power source quality in an elevator system.
An elevator drive system is typically designed to operate over a specific input voltage range from a power source. The components of the drive have voltage and current ratings that allow the drive to continuously operate while the power supply remains within the designed input voltage range. However, in certain markets the utility network is less reliable, where persistent utility voltage sags or brownout conditions (i.e., voltage conditions below the tolerance band of the drive) and/or over-voltage conditions are prevalent. These changes in the voltage levels in a power system are collectively known as power quality events. When utility voltage sags occur, the drive draws more current from the power supply to maintain uniform power to the hoist motor. In conventional systems, when excess current is being drawn from the power supply, the drive will shut down to avoid damaging the components of the drive. In addition, when an over-voltage condition occurs, the components of the elevator system may be damaged when they are forced to operate above their power tolerance band. This can lead to component deterioration and failure, resulting in the need for repair or replacement of the damaged components.